Process for the preparation of alpha,omega-alkanediol mononitrate

ABSTRACT

The invention relates to a safe and efficient process for the hydrolysis of α,ω-C3-10alkanediol mononitrate monoacylates. The process is safer to operators and allows to obtain advantageous yields on industrial scale.

The invention relates to a safe and efficient process for themanufacture of ω-nitrooxy-C₃₋₁₀alkane-1-ols.

Global temperature is increasing, a process referred to as globalwarming or climate change. One of the main focuses to reduce thiswarming effect is to reduce the amount of greenhouse gases emitted intothe atmosphere. Greenhouse gases are emitted from several differentsources, both natural and anthropogenic; however, the two sources withthe biggest impact are the agricultural and fossil fuel industries.Within agriculture, ruminants and in particular cattle are the majorcontributors to the biogenic methane formation, and it has beenestimated that the prevention of methane formation from ruminants wouldalmost stabilize atmospheric methane concentrations.

3-Nitrooxypropanol (3-NOP, also known as 3-nitrooxy-propan-1-ol or1,3-propanediol mononitrate) has been reported to be highly efficient inreducing the formation of methane in ruminants without affectingmicrobial fermentation in a way that would be detrimental to the hostanimal (WO-2012/084629). Furthermore, WO-2012/084629 discloses thepreparation of 3-nitrooxypropanol by reacting 3-bromopropanol inacetonitrile with silver nitrate, a process which is, however, noteconomical in industrial scale production.

A potential route for industrial scale production ofω-nitrooxy-C₃₋₁₀alkane-1-ols involves direct nitrate ester formation ofthe respective α,ω-alkanediols. This reaction, however, is often poorlyselective and leads to the formation of significant amounts ofdinitrated alkanediols. Furthermore, this route requires high safetymeasures since organic nitrates and even more dinitrates are explosiveand therefore difficult to handle, even in diluted solution.

An alternative to the direct nitrate ester formation of α,ω-alkanediolsis a three-step process encompassing the interim protection of one ofthe two alcohol groups prior to nitrate ester formation, e.g. byacetylation, followed by nitrate ester formation and consecutive removalof the respective protecting group after the nitrate ester formationstep. However, even though the safety and the selectivity may thus beincreased, the additional reaction steps normally lead to a significantloss in the overall yield and a substantial increase in processing cost.

Thus, there is an ongoing need for the optimization of the three-stepprocess allowing safe and economical production ofω-nitrooxy-C₃₋₁₀alkane-1-ols in large quantities starting fromα,ω-alkanediols. Furthermore, there is a need for workup strategies toallow a quantitative recovery of reactants as well as solvents.

Surprisingly it has now been found that ω-nitrooxy-C₃₋₁₀alkane-1-olssuch as in particular 3-nitrooxypropanol can be obtained in high yieldsin a highly specialized three-step process, while at the same timemaintaining the reaction stability and thus ensuring process safety.

Said process encompasses the consecutive steps of (a) acylation of thecorresponding α,ω-alkanediol with an acylating agent, (b) nitrate esterformation of the resulting α,ω-C₃₋₁₀ alkanediol monoacylate with anitrating agent to form a α,ω-C₃₋₁₀alkanediol mononitrate monoacylatefollowed by (c) hydrolysis of the acyl group to obtain the respectiveα,ω-C₃₋₁₀alkanediol mononitrate and optionally (d) solvent work-up.

The individual steps (a) to (d) are novel.

Thus, in a first embodiment, the present invention relates to

-   -   (C) A continuous process for the two-phase hydrolysis of an        α,ω-C₃₋₁₀alkanediol mononitrate monoacylate, preferably        1,3-propanediol mononitrate monoacetate, said process comprising        continuously feeding a base and a solution comprising the        α,ω-C₃₋₁₀alkanediol mononitrate monoacylate and an inert        solvent, preferably an inert halogenated solvent, such as in        particular dichloromethane (DCM), into a stirred cascade        reactor.

In a further embodiment the present invention relates to a process forthe preparation of an α,ω-C₃₋₁₀alkanediol mononitrate, preferably ofpropanediol mononitrate, said process comprising next to step (C)outlined above the following steps: (A) and (B) before and optionally(D) after said step (C), said steps being

-   -   (A) Acylation of an α,ω-alkanediol with an acylation agent        (acylation reaction), said acylation comprising the step of        re-feeding recycled reaction components comprising        α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate and        α,ω-C₃₋₁₀alkanediol diacylate back into said acylation reaction,        with the proviso that in the acylation reaction per mole        recycled acylate groups 0.5 to 1.5 mole of water is present and        that the molar ratio of the (molar) sum of the acylating agent,        α,ω-C₃₋₁₀alkanediol monoacylate and 2 times of        α,ω-C₃₋₁₀alkanediol diacylate to the sum of the        α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate and        α,ω-C₃₋₁₀alkanediol diacylate is selected in the range 0.5 to        1.1 mol per mol of α,ω-C₃₋₁₀alkanediol, preferably in the range        from 0.6 to 1 mol, most preferably in the range from 0.75 to 1        mol,    -   (B) Continuous nitrate ester formation of the        α,ω-C₃₋₁₀alkanediol monoacylate by reacting a nitrating agent        with a solution comprising the α,ω-C₃₋₁₀alkanediol monoacylate        and an inert solvent in a group of pieces of equipment        comprising at least two reactors in series by simultaneously        feeding said solution into the first and the second reactor to        obtain the respective α,ω-C₃₋₁₀ alkanediol mononitrate        monoacylate,    -   (D) Removal and recovery of the inert solvent from the solution        by distillation, said distillation comprising partial        condensation and continuous back-feeding of liquid fractions        comprising mixtures of inert solvent and α,ω-C₃₋₁₀ alkanediol        mononitrate into said distillation.

Definition of Terms

The term ‘α,ω-C₃₋₁₀alkanediols’ as used herein refers to linearα,ω-alkanediols having 3 to 10 carbon atoms such as 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol and 1,10-decanediol. The most preferredα,ω-C₃₋₁₀alkanediol in all embodiments according to the presentinvention is 1,3-propanediol (also referred to herein as PD).

The term ‘α,ω-C₃₋₁₀alkanediol monoacylate’ as used herein refers to thelinear α,ω-alkanediols as defined above, wherein one of the hydroxylgroups has been esterified. Preferably, the acyl moiety is a linear orbranched C₁₋₆ acyl group, more preferably a linear or branched C₁₋₄ acylgroup such as most preferably acetyl (—C(═O)—CH₃). Particularlypreferred in all embodiments according to the present invention are the1,3-propanediol monoacylates. The most preferred α,ω-C₃₋₁₀alkanediolmonoacylate in all embodiments of the present invention is1,3-propanediol monoacetate (also referred to herein as PDMA).

The term ‘α,ω-C₃₋₁₀alkanediol diacylate’ as used herein refers to thelinear α,ω-alkanediols as defined above, wherein both of the hydroxylgroups have been esterified. Particularly preferred in all embodimentsaccording to the present invention are the 1,3-propanediol diacylates.The most preferred α,ω-C₃₋₁₀alkanediol diacylate in all embodiments ofthe present invention is 1,3-propanediol diacetate (also referred toherein as PDDA).

The term ‘α,ω-C₃₋₁₀alkanediol mononitrate’ as used herein refers to thelinear α,ω-alkanediols as defined above wherein one of the hydroxylgroups has been nitrated such 3-nitrooxypropane-1-ol (also referred toas 3-nitrooxypropanol or 3-hydroxypropyl-1-nitrate),4-nitrooxybutane-1-ol, 5-nitrooxypentane-1-ol, 6-nitrooxyhexane-1-ol,7-nitrooxyheptane-1-ol, 8-nitrooxyoctane-1-ol, 9-nitrooxynonane-1-ol and10-nitrooxydecane-1-ol. Particularly preferred in all embodimentsaccording to the present invention is 3-nitrooxypropane-1-ol (alsoreferred to herein as propanediol mononitrate or PDMN).

The term ‘α,ω-C₃₋₁₀alkanediol mononitrate monoacylate’ as used hereinrefers to the α,ω-C₃₋₁₀alkanediol monoacylates as defined above whereinthe remaining hydroxyl group has been nitrated. Particularly preferredin all embodiments according to the present invention are the1,3-propanediol mononitrate monoacylates. The most preferredα,ω-C₃₋₁₀alkanediol mononitrate monoacylate in all embodiments accordingto the present invention is 1,3-propanediol mononitrate monoacetate(also referred herein to as PDMNMA).

The term ‘α,ω-alkanedioldinitrates’ as used herein refers to the linearα,ω-alkanediols as defined above wherein both hydroxyl groups have beennitrated, such as 1,3-propanediol dinitrate, 1,4-butanediol dinitrate,1,5-pentanediol dinitrate, 1,6-hexanediol dinitrate, 1,7-heptanedioldinitrate, 1,8-octanediol dinitrate, 1,9-nonanediol dinitrate and1,10-decanediol dinitrate. Particularly preferred in all embodimentsaccording to the present invention is 1,3-propanediol dinitrate (alsoreferred herein to as PDDN).

The term ‘inert solvent’ (also abbreviated as ‘S’) as used herein isunderstood as meaning a solvent which does not take part in a chemicalreaction in the reaction medium and under the operating conditions, andwhich is inert to both the reactants and the reaction products. In apreferred embodiment, the inert solvent is a halogenated solvent. Theterm ‘halogenated solvent’ means a solvent containing one or morehalogen atoms and refers to any solvent selected from, but is notlimited to, dichloromethane, diiodomethane, carbon tetrachloride,dichloroethane, or chloroform. Most preferably in all embodiments of thepresent invention, the inert solvent is dichloromethane (also referredto herein as DCM).

The term ‘consisting essentially of’ as used according to the presentinvention means that besides the listed components/ingredients/solventsetc. no further components are purposively added. It is however notexcluded that small amount of impurities introduced by the respectiveraw materials may be present.

Hydrolysis

The present invention relates to a process for a two-phase hydrolysis ofan α,ω-C₃₋₁₀alkanediol mononitrate monoacylate (to the respectiveα,ω-C₃₋₁₀alkanediol mononitrate), preferably of 1,3-propanediolmononitrate monoacetate to 1,3-propanediol mononitrate, said processcomprising continuously feeding a base and a solution comprising anα,ω-C₃₋₁₀alkanediol mononitrate monoacylate and an inert solvent such asin particular dichloromethane (DCM) into a stirred cascade reactor.

In the following, the solution comprising an α,ω-C₃₋₁₀alkanediolmononitrate monoacylate and an inert solvent is also referred to as HS-I(e.g. in FIG. 3 ).

The hydrolysis processes according to the present invention can becarried out batch wise or continuously. Preferably, the hydrolysisprocess is a (fully) continuous process.

In a particular advantageous embodiment, said hydrolysis processcomprises the following consecutive steps:

-   -   (H-1) Provision of a vertical, stirred cascade reactor setup,    -   (H-2) Continuous feeding of a solution comprising an        α,ω-C₃₋₁₀alkanediol mononitrate monoacylate and an inert solvent        together with a base to the first (bottom) chamber (hydrolysis        reactor C1 in FIG. 3 ),    -   (H-3) Transferring the hydrolysis reaction mixture (also        referred to herein as HRM) comprising α,ω-C₃₋₁₀alkanediol        mononitrate, the inert solvent and the remaining base solution        into a decanter or vessel (FIG. 3 : C2) for phase separation to        obtain an organic solution (I) comprising the        α,ω-C₃₋₁₀alkanediol mononitrate and the inert solvent (also        referred to herein as HS-II) and an aqueous solution (also        referred to herein as HS-III), followed by    -   (H-4) Collecting the organic solution (I) comprising the        α,ω-C₃₋₁₀alkanediol mononitrate and the inert solvent (i.e.        HS-II), optionally followed by    -   (H-5) Evaporating the inert solvent from the organic        solution (I) by distillation.

An exemplary (while preferred) hydrolysis according to the presentinvention is illustrated in FIG. 3 .

In a preferred embodiment, the hydrolysis process according to thepresent invention further contains an additional step (H-6), comprisingthe steps

-   -   (H-6a) extracting the aqueous phase (HS-II) obtained in step        (H-3) with an additional amount of the inert solvent to recover        further α,ω-C₃₋₁₀alkanediol mononitrate to yield an additional        organic phase (II) (also referred to herein as HS-IV), and    -   (H-6b) Co-feeding said organic phase (II) into step (H-5).

The hydrolysis process is preferably carried out in (continuously) in avessel cascade set-up or a cascade reactor, more preferably in avertical, stirred cascade reactor. In a preferred embodiment of theinvention, the hydrolysis process is performed in a vertical, stirredcascade reactor with at least 10 chambers.

For the purpose of hydrolysis process a vertical, stirred cascadereactor is a vertical reactor, that is also a stirred reactor. The term“vertical reactor” or “horizontal reactor vessel”, as used herein, meansa reactor vessel having a longitudinal axis which is substantiallyvertical. The term “stirred reactor” as used herein, means a reactorhaving a means for agitating the reaction material in addition to theagitation caused by the flow (e.g., turbulent flow of the reactionmaterial).

In a preferred embodiment of the present invention, the base used forthe hydrolysis reaction of the α,ω-C₃₋₁₀alkanediol mononitratemonoacylate is aqueous NaOH, the concentration of which in water ispreferably selected in the range from 1 and 50 wt.-%, more preferablyfrom 5 and 30 wt.-%, most preferably from 7.5 and 15 wt.-%.

Advantageously, the reaction temperature for the hydrolysis reaction isselected in the range from 20 to 70° C., preferably from 30 to 60° C.,most preferably from 40 to 60° C.

It is furthermore advantageous that 1 to 1.5 mol equivalents, morepreferably 1.1 to 1.3 mol equivalents and most preferably 1.2 to 1.3 molequivalents of base, preferably NaOH, based on the α,ω- C₃₋₁₀alkanediolmononitrate monoacylate, is used for the hydrolysis reaction.

The hydrolysis reaction is preferably carried out for a reaction timeranging from about 2 to about 6 hours, preferably from about 3 to about5 hours, most preferably for about 4 hours.

Acylation

In a preferred embodiment, the process according to the presentinvention also comprises a step (A) which precedes step (C), which step(A) is directed to the acylation of an α,ω-alkanediol with an acylationagent (acylation reaction), said acylation comprising the step ofre-feeding recycled reaction components into said acylation reaction asoutlined above.

It is well understood, that the acylation may further comprise the stepsof isolation and/or purification of the obtained α,ω-C₃₋₁₀alkanediolmonoacylate by the methods disclosed herein or any other suitable methodin the art.

It is well understood, that the term ‘reaction components’ as usedherein refers to components of the acylation reaction which take part inthe acylation reaction, i.e. the α,ω-alkanediol, the α,ω-C₃₋₁₀alkanediolmonoacylate and the α,ω-C₃₋₁₀alkanediol diacylate as well as theacylating agent and water, not encompassing, however, any solvents orother inert ingredients or additives.

In all embodiments of the present invention, the term ‘recycled reactioncomponents’ (also abbreviated as RRC) refers to unreactedα,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate andα,ω-C₃₋₁₀alkanediol diacylate as well as water and acylating agent.

It is furthermore well understood, that the recycled reaction componentscan be isolated separately or as any mixture thereof and thus be re-fedindividually or as any mixture thereof. Preferably, the recycledreaction components consist essentially of

-   -   (1) a mixture of α,ω-C₃₋₁₀alkanediol monoacylate and        α,ω-C₃₋₁₀alkanediol diacylate (RCC-(I))    -   (2) unreacted α,ω-C₃₋₁₀alkanediol (RCC-(ll)) as well as    -   (3) a mixture of water and acylating agent (RCC-(III)).

In all embodiments of the present invention it is preferred that atleast the recycled reaction components RCC-(I) and RCC-(II) are admixedbefore being re-fed into the acylation reaction (see FIG. 1 ).

The acylation according to the present invention can be carried outbatch wise or continuously.

Preferably, the acylation of the α,ω-alkanediols with an acylation agentaccording to the present invention is carried out in a reactor intowhich the recycled reaction components are (continuously) re-fed.

Suitable reactors include any type of vessel, such as stirred tankreactors, cascade reactors, loop reactors, tubular reactors, withoutbeing limited thereto.

In a particular embodiment, the acylation according to the presentinvention further comprises the step of separation of the obtainedα,ω-C₃₋₁₀alkanediol monoacylate by distillation, preferably in a waysuch that

-   -   the amount of α,ω-C₃₋₁₀alkanediol in the α,ω-C₃₋₁₀alkanediol        monoacylate is less than 0.5 wt.-%, preferably less than 0.1        wt.-%, based on the α,ω-C₃₋₁₀alkanediol monoacylate and    -   the amount of the α,ω-C₃₋₁₀alkanediol diacylate in the        α,ω-C₃₋₁₀alkanediol monoacylate is less than 5 wt. %, preferably        less than 2.5 wt.-%, based on the α,ω-C₃₋₁₀alkanediol        monoacylate.

It is furthermore preferred that during said separation the reactioncomponents to be recycled are collected.

Preferably, in all embodiments of the present invention, the acylationand the consecutive separation of the α,ω-C₃₋₁₀alkanediol monoacylate isa (fully) continuous process carried out in a vessel cascade set-up or acascade reactor as e.g. outlined in FIG. 1 ).

A vessel cascade set-up (also called reactor cascade set-up) for thepurpose of the invention is a setup that comprises at least twoconsecutive vessels, in which the reaction can be performed and whereineach step can only be performed after the previous one. Thevessels/reactors can be of the same or different types. It is wellunderstood by a person skilled in the art that the vessel cascade set-upmay include devices for separation and/or distillation.

A cascade reactor for the purpose of the invention is a setup thatcomprises an outer reactor shell with at least one inlet at one end andat least one outlet at the opposite end, optional additional outlets forvapor and/or by-product removal, and optional ports for monitoring,sampling and/or mixing. Within the reactor, a series of two or moresegmented reaction chambers (corresponding to at least two consecutivevessels) may be defined by partitions, in which the reaction can beperformed and wherein each chamber/partition can only be flown throughafter the previous one. The reactor is preferably suitable for multipledifferent chemical reactions and need not be custom-made for aparticular reaction. The cascade reactor may, for example be a flowreactor.

In a particular embodiment of the present invention, the acylation(including the subsequent separation of the obtained α,ω-C₃₋₁₀alkanediolmonoacylate) is a process encompassing the steps of

-   -   (A-1) Acylation of an α,ω-C₃₋₁₀,1kanediol with an acylating        agent (acylation reaction) in an initial vessel, with the        proviso that in said acylation reaction per mole recycled        acylate groups 0.5 to 1.5 mole of water is present and the molar        ratio of the (molar) sum of the acylating agent,        α,ω-C₃₋₁₀alkanediol monoacylate and 2 times of        α,ω-C₃₋₁₀alkanediol diacylate to the sum of the        α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate and        α,ω-C₃₋₁₀alkanediol diacylate is selected in the range from 0.5        to 1.1 mol per mol of α,ω-C₃₋₁₀alkanediol (also referred to as        acetylation reaction mixture or ARM),    -   (A-2) Removal of the acylating agent and water to form a mixture        comprising unreacted α,ω-C₃₋₁₀alkanediol as well as mono- and        diacylated α,ω- C₃₋₁₀alkanediol (also referred to as AM-I),    -   (A-3) Separation of the α,ω-C₃₋₁₀alkanediol monoacylate from        said mixture (i.e. from AM-I) by distillation such that the thus        obtained α,ω-C₃₋₁₀alkanediol monoacylate contains less than 0.5        wt.-% of α,ω-C₃₋₁₀alkanediol and less than 5 wt.-% of        α,ω-C₃₋₁₀alkanediol diacylate,    -   (A-4) Collecting the reaction components to be recycled, and    -   (A-5) Re-feeding the recycled reaction components comprising at        least α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate and        α,ω-C₃₋₁₀alkanediol diacylate into the initial vessel.

In all embodiments of the present invention it is preferred that withinthe acylation reaction, such as in particular in step (A-1)

-   -   per mole recycled acylate groups preferably 0.75 to 1.25 mole,        most preferably 0.85 to 1.1 mole such as in particular 0.95 to        1.05 mole of water is present, and    -   the molar ratio of the (molar) sum of the acylating agent,        α,ω-C₃₋₁₀alkanediol monoacylate and 2 times α,ω-C₃₋₁₀alkanediol        diacylate to the sum of the α,ω-C₃₋₁₀alkanediol,        α,ω-C₃₋₁₀alkanediol monoacylate and α,ω-C₃₋₁₀alkanediol        diacylate is preferably selected in the range from 0.6 to 1 mol,        most preferably in the range from 0.7 to 1 mol, such as in        particular in the range from 0.75 to 1 mol.

The term ‘per mole acylate groups’ as used herein refers to the sum ofacylate groups from the α,ω-C₃₋₁₀alkanediol monoacylate and theα,ω-C₃₋₁₀alkanediol diacylate (i.e. 1 mol for each α,ω-C₃₋₁₀alkanediolmonoacylate and two moles for each α,ω-C₃₋₁₀alkanediol diacylate).

As already outlined above, the reaction components to be recycled instep (A-5) consist essentially of α,ω-C₃₋₁₀alkanediol,α,ω-C₃₋₁₀alkanediol monoacylate and α,ω-C₃₋₁₀alkanediol diacylate.However, it is not excluded by the present invention that the acylatingagent and/or the water removed in step (A-2) can also be recycled andre-fed as deemed appropriate.

It is furthermore well understood, that, to adjust the ratios andamounts as defined herein, fresh α,ω-C₃₋₁₀alkanediol, water and/oracylating agent are added as needed.

Suitable acylating agents (also referred to herein to as AA) for theacylation processes according to the present invention are carboxylicacids and derivatives thereof such as e.g. the respective, esters andacyl halides thereof. Preferably, the acylating agent is selected fromthe group consisting of linear or branched C₁₋₆ alkanoic acidsrespectively, esters or acid chlorides thereof, more preferably fromlinear C₁₋₄ carboxylic acids such as for example acetic acid, propanoicacid, butanoic acid and pentanoic acid. The most preferred acylatingagent is acetic acid. Any acetic acid, i.e. also aqueous solutionsthereof can be used in all embodiments of the acylation. It is howeverunderstood, that the water content has to be adjusted accordingly tocomply with the requirements according to the present invention.

The reaction temperature for the acylation reaction is preferablyselected in the range from 80 to 200° C., more preferably in the rangefrom 100 to 160° C., most preferably in the range of 120 to 150° C. Itis well understood, that the pressure has eventually to be adjustedaccording to the desired reaction temperature.

The reaction time for the acylation reaction (such as in particular instep (A-1)) is preferably selected in the range from 1 to 10 hours,preferably in the range from 2 to 8 hours, most preferably in the rangefrom 3 to 6 hours.

The removal of the acylation agent and reaction water in step (A-2) ispreferably performed by distillation at reduced pressure and heating,which can be easily adjusted by a person skilled in the art. Suitablepressures include 40 to 120 mbar abs.

The separation of the α,ω-C₃₋₁₀alkanediol monoacylate from the reactionmixture (i.e. from AM-I) is preferably performed such, that the amountof α,ω-C₃₋₁₀alkanediol diacylate therein is less than 4 wt.-%, morepreferably less than 3 wt.-%, most preferably less than 2.5 wt.-% suchas less than 1 wt.-%, and the amount of the respectiveα,ω-C₃₋₁₀alkanediol therein is less than 0.4 wt.-%, more preferably,less than 0.25 wt.-%, most preferably less than 0.2 wt.-%, such as inparticular less than 0.1 wt.-% (all amounts based on the amount of theα,ω-C₃₋₁₀alkanediol monoacylate).

The amount of residual α,ω-C₃₋₁₀alkanediol diacylate andα,ω-C₃₋₁₀alkanediol in the isolated (distilled) α,ω-C₃₋₁₀alkanediolmonoacylate is generally determined by GC chromatography using a FIDdetector.

In a particularly advantageous embodiment, the separation/purificationof the α,ω-C₃₋₁₀alkanediol monoacylate (i.e. Step (A-3)) is performed intwo consecutive steps, i.e.

-   -   Step (A-3′) consisting of distilling off the majority of the        α,ω-C₃₋₁₀alkanediol diacylate from the mixture (AM-I) obtained        in step (A-2) until a mixture (AM-Ia) is obtained, which        consists essentially of α,ω-C₃₋₁₀alkanediol and        α,ω-C₃₋₁₀alkanediol monoacetate followed by    -   Step (A-3″) consisting of distilling off the α,ω-C₃₋₁₀alkanediol        monoacylate from the mixture (AM-Ia) such that the amount of        α,ω-C₃₋₁₀alkanediol in the distilled α,ω-C₃₋₁₀alkanediol        monoacetate is as defined herein, while preferably recovering        unreacted α,ω-C₃₋₁₀alkanediol.

The term consisting essentially in Step (A-3′) does not exclude thepresence of small amounts of α,ω-C₃₋₁₀alkanediol diacetate, whichamounts however have to be controlled such, that the final amount ofα,ω-C₃₋₁₀alkanediol diacetate in the α,ω-C₃₋₁₀alkanediol monoacetate isas defined herein. Preferably, said amount does however not exceed 3mole.-%.

It is even more preferred, that step (A-3′) and step (A-3″) areperformed in two distinct vessels (distillation set-ups).

In an even more preferred embodiment step (A-3′) and step (A-3″) areperformed using two separate distillation columns.

In a particular embodiment, the mixture (AM-I) consists essentially of40 to 60 mol-% of α,ω-C₃₋₁₀alkanediol, 30 to 50 mol-% ofα,ω-C₃₋₁₀alkanediol monoacylate and 5-15 mol-% α,ω-C₃₋₁₀alkanedioldiacylate.

In another particular embodiment, the mixture (AM-Ia) consistsessentially of 50 to 70 mol-% of α,ω-C₃₋₁₀alkanediol and 30 to 50 mol-%of α,ω-C₃₋₁₀alkanediol monoacylate and up to 3 mol.-% ofα,ω-C₃₋₁₀alkanediol diacylate.

The reaction components to be recycled, i.e. which are re-fed into theacylation reaction such as in particular into step (A-1) above generallyconsist of the distillate of step (A-3′) consisting essentially ofα,ω-C₃₋₁₀alkanediol monoacylate and α,ω-C₃₋₁₀alkanediol diacylate andthe sump of step (A-3″) consisting essentially of unreactedα,ω-C₃₋₁₀alkanediol.

Preferably, the distillate of step (A-3′) consists essentially of 10 to40 wt.-% of α,ω-C₃₋₁₀alkanediol monoacylate and 60 to 90 wt.-% ofα,ω-C₃₋₁₀alkanediol diacylate and up to 5 wt.-% α,ω-C₃₋₁₀alkanediol.

Preferably the sump of step (A-3″) consists essentially of more than 95wt.-% of α,ω-C₃₋₁₀alkanediol, more preferably of more than 97 wt. %,most preferably of more than 99 wt.-%.

The α,ω-C₃₋₁₀alkanediol monoacylate obtained in step (A-3″) preferablyexhibits a purity of more than 95 wt.-%, preferably of more than 97wt.-%, most preferably of more than 98.5 wt.-% as determined by GCanalysis using a FID detector.

In a particular advantageous embodiment of the present invention, theacylation (including the subsequent separation of the obtainedα,ω-C₃₋₁₀alkanediol monoacylate) is a process as outlined in FIG. 1encompassing the steps of

-   -   (A-0) Provision of a vessel cascade setup,    -   (A-1′) Acylation of the α,ω-C₃₋₁₀alkanediol with an acylating        agent with all the definitions and preferences as given herein        by loading the first vessel (V1) with the α,ω-C₃₋₁₀alkanediol,        the acylating agent and the recycled reaction components to form        a reaction mixture (ARM), followed by    -   (A-2′) Feeding the reaction mixture (ARM) onto a first        distillation column (V2) and distilling off the acylating agent        and water to form a mixture (AM-I) consisting essentially of        unreacted α,ω-C₃₋₁₀alkanediol and mono- and diacylated        α,ω-C₃₋₁₀alkanediol, followed by    -   (A-3′) Feeding the mixture (AM-I) onto a second distillation        column (V3) and distilling off a mixture of α,ω-C₃₋₁₀alkanediol        mono and diacylate (i.e. RRC-(I)) to form a mixture (AM-Ia)        consisting essentially of α,ω-C₃₋₁₀alkanediol and        α,ω-C₃₋₁₀alkanediol monoacetate,    -   (A-3″) Feeding the mixture (AM-Ia) onto a third distillation        column (V4) and distilling off the α,ω-C₃₋₁₀alkanediol        monoacylate such that the amount of α,ω-C₃₋₁₀alkanediol in the        distilled α,ω-C₃₋₁₀alkanediol monoacetate is less than 0.1 wt.-%        and while recovering the α,ω-C₃₋₁₀alkanediol from the sump (i.e.        RCC-(II)),    -   (A-4′) Collecting and optionally mixing the reaction components        to be recycled, and    -   (A-5′) Re-feeding the optionally admixed recycled reaction        components RRC-(I) and RRC-(II) from step (iv) and (v) into the        first reaction vessel (V1),    -   with the proviso that in the first reactor vessel        -   (a) per mole recycled acylate groups 0.5 to 1.5 mole,            preferably 0.75 to 1.25 mole, most preferably 0.85 to 1.1            mole, such as in particular 0.95 to 1.05 mole of water is            present, and        -   (b) the molar ratio of the (molar) sum of the acylating            agent, α,ω-C₃₋₁₀alkanediol monoacylate and 2 times of            α,ω-C₃₋₁₀alkanediol diacylate to the sum of the            α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate and the            α,ω-C₃₋₁₀alkanediol diacylate is adjusted in the range 0.5            to 1.1 mol per mol of α,ω-C₃₋₁₀alkanediol, preferably in the            range from 0.6 to 1 mol, most preferably in the range of 0.7            to 1 mol such as in the range from 0.75 to 1 mol.

It is well understood, that the recycled reaction components (I) maycontain α,ω-C₃₋₁₀alkanediol monoacylate such as in amounts of up to 45wt.-% as determined by e.g. GC-analysis using FID detector.

Preferably, in all embodiments the recycled reaction components (II)consists of more than 90 wt.-% of α,ω-C₃₋₁₀alkanediol, more preferablyof more than 95 wt. %, most preferably of more than 98 wt.-% ofα,ω-C₃₋₁₀alkanediol, as determined by e.g. GC-analysis using a FIDdetector.

It is, of course, well understood, that all the definitions andpreferences for the acylation (including the acylation reaction andseparation) herein also apply to the processes comprising the steps(A-1) to (A-5) as well as (A-0) to (A-5′).

Nitrate Ester Formation

In a preferred embodiment, the process according to the presentinvention also comprises a step (B), following step (A) and precedingstep (C) directed to a continuous nitrate ester formation process forthe preparation of α,ω-C₃₋₁₀alkanediol mononitrate monoacylates, saidprocess comprising reacting a nitrating agent with a solution comprisingthe respective α,ω-C₃₋₁₀alkanediol monoacylate and an inert solvent (inthe following also referred to as (B-I)) in a group of pieces ofequipment comprising at least two reactors in series, characterized inthat the solution is simultaneously fed into the first (also referred toas reactor B1) and the second (also referred to as reactor B2) reactor(see FIG. 2 ).

Preferably, the nitrate ester formation is carried out continuously in aflow-reactor as e.g. depicted in FIG. 2 .

A flow reactor according to this invention is a device in which chemicalreactions take place in channels or tubes. The flow reactor is generallyoperated continuously (in contrast with/to a batch reactor) and haschannels/tubes in which the reaction takes place (such as the reactorsB1 and B2 in FIG. 2 ). The reaction stoichiometry is defined by theconcentration of reagents and the ratio of their flow rate. The (mean)residence time is given by the ratio of volume of the reactor and theoverall flow rate. The flow reactor preferably comprises (static) mixingelements, such as SMX mixer or Kenics mixer.

The term “residence time” as used herein refers to the volume of thereaction zone divided by the outlet volumetric flow rate of reactants atthe reaction system's temperature and pressure. In a specific embodimentof the invention the mean residence time is calculated with the densityof the respective outlet temperature of the reactor.

Preferably, the mass flow ratio of the solution (B-I) into the firstreactor is selected in the range of 40 to 60% of the total mass flow ofthe solution (B-I), the remaining is fed to the second reactor.

The term “mass flow” or “mass flow rate” as used herein may include notonly the actual or measured mass flow rate, but also the calculated massflow rate. It generally refers to the mass flow rate of a reactionsolution as measured in the corresponding feed lines. This mass flowrate can be calculated or measured with a suitable sensor located in thecorresponding feed lines.

In a particular advantageous embodiment the continuous nitrate esterformation according to the present invention comprises the followingconsecutive steps:

-   -   (N-1) Provision of a continuously operated flow-reactor        comprising at least two reactors, reactor (1) (also referred to        herein as B1) and reactor (2) (also referred to herein as B2),        in series    -   (N-2) Provision of a solution comprising an α,ω-C₃₋₁₀alkanediol        monoacylate and an inert solvent (i.e. B-I), and    -   (N-3) Feeding of reactor (1) with a nitrating agent and a first        portion of said solution, followed by    -   (N-4) Adding a second portion of said solution into the reactor        (2), with the proviso that the mass flow of the solution into        the reactor 1 is selected in the range of 40 to 60% of the total        mass flow of the solution, while the remaining solution is fed        into reactor 2.

The term “nitrating agent” (also referred to herein as NA) as usedherein refers to a compound which when reacted with a reactant substrateforms a compound with a nitrate ester (—O—NO₂) group. Exemplarynitrating agents include, but are not limited to, nitric acid andnitrate salts, such as alkali metal nitrate salts, e.g., KNO₃, as wellas nitrosulfuric acid (i.e. a mixture of nitric acid and sulphuric acid)

In all embodiments of the present invention, the nitrating agent ispreferably nitric acid applied as nitrosulfuric acid, i.e. a mixture ofnitric acid and sulphuric acid.

In the continuous nitrate ester formation according to the presentinvention, preferably 1.5 to 2.5 mol equivalents, more preferably 1.7 to2.3 mol equivalents, most preferably 1.9 to 2.0 mol equivalents ofH₂SO₄, based on HNO₃ is used.

In the continuous nitrate ester formation according to the presentinvention, preferably from 1 to 1.5 mol equivalents, more preferablyfrom 1.1 to 1.2 mol equivalents of HNO₃, based on theα,ω-C₃₋₁₀alkanediol monoacylate is used.

In the continuous nitrate ester formation according to the presentinvention it is furthermore preferred that the reaction volume of thereactor (1) to the reactor (2) is selected in the range from 4:1 to 1:4,preferably from 3:1 to 1:3, most preferably from 2:1 to 1:2.

The continuous nitrate ester formation is preferably carried out for amean residence time in both reactors (i.e. in reactor (1) and reactor(2) (FIG. 2 : in B1 and B2) ranging from about 5 to about 30 seconds,preferably from about 10 to about 20 seconds, most preferably from about15 to 19 seconds.

Preferably in all embodiments of the continuous nitrate ester formation,the solution (i.e. B-I) consists essentially of the α,ω-C₃₋₁₀alkanediolmonoacylate and the inert solvent.

The term ‘consisting essentially of’ as used according to the presentinvention means that besides the listed components/ingredients/solventsno further components are purposively added. It is however not excludedthat small amount of impurities introduced by the respective rawmaterials may be present.

Even more preferably, the concentration of the α,ω-C₃₋₁₀alkanediolmonoacylate in the inert solvent is selected in the range from 10 and 60wt.-%, more preferably from 20 and 50 wt.-% and most preferably from 35and 45 wt.-%, the remainder being the inert solvent.

In a particular advantageous embodiment the continuous nitrate esterformation according to the present invention further comprises thefollowing steps:

-   -   (N-5a) Quenching (in B3) the reaction mixture (also referred to        herein as NRM) with water, optionally in the presence of a base        resulting in a biphasic mixture (also referred to herein as NBM)        consisting of an organic and aqueous phase,    -   (N-5b) Phase separation (in B4) of the biphasic mixture (NBM) to        obtain an organic (also referred to herein as NOP) and an        aqueous phase (also referred to herein as NAP),    -   (N-5c) optionally Concentrating the aqueous phase (NAP) from        phase separation to recover H₂SO₄ if no base was used for        neutralization, and    -   (N-5d) optionally Washing the organic phase (NOP) obtained in        (N-5c) at least once with water and/or drying the organic phase.

A particularly preferred continuous nitrate ester formation is outlinedin FIG. 2 , which continuous nitrate ester formation consists of theconsecutive steps (N-1), (N-2), (N-3), (N-4), (N-5a), (N-5b) and (N-5c).

It is well understood that the continuous nitrate ester formationaccording to the present invention may also comprise the step ofisolating/concentrating the α,ω-C₃₋₁₀alkanediol mononitrate monoacylatefrom the organic phase (NOP) e.g. by (partial) distillation of thesolvent.

The nitrate ester formation reaction mixture (NRM) in all embodiments ofthe present invention preferably consists essentially of theremaining/unreacted nitrating agent, α,ω-C₃₋₁₀alkanediol mononitratemonoacylate, unreacted α,ω-C₃₋₁₀alkanediol monoacylate and inertsolvent.

Suitable bases include alkali or earth alkali bases such as alkali orearth alkali hydroxides or carbonates as well as ammonia, amines withoutbeing limited thereto. The base is preferably selected from the group ofNaOH (caustic), KOH, Ca(OH)₂ or ammonia, more preferably an aqueoussolution thereof is used. Most preferably in all embodiments of thepresent invention the base is aqueous NaOH (caustic).

In the continuous nitrate ester formation according to the presentinvention preferably no base is used for quenching.

Thus, in a further particular advantageous embodiment, the quenching ofthe nitrate ester formation reaction mixture (NRM) is performed eitherwith cold water, such as with water having a temperature selected in therange from 0 to 20° C., more preferably in the range from 5 to 15° C.

In the continuous nitrate ester formation according to the presentinvention, advantageously, the outlet reaction temperature of thereactor (1) is equal to or below 40° C., preferably 30° C., morepreferably 20° C., more preferably 10° C. and most preferably equal toor below 5° C. The outlet reaction temperature of reactor (2) can beslightly higher. Preferably, however the outlet temperature of reactor(2) is selected in the range of 15 to 25° C.

Advantageously, in all embodiments, the reaction temperature for thequenching step (N-6a) is equal to or below 20° C., preferably equal toor below 15° C., more preferably equal to or below 10° C.

Removal and Recovery of the Inert Solvent

In a further preferred embodiment, the process according to the presentinvention further comprises a step (D) (following step (C) directed to aprocess for removal and recovery of an inert solvent from a mixturecomprising the inert solvent and an α,ω-C₃₋₁₀alkanediol mononitrate bydistillation, said process comprising partial evaporation andcondensation and continuous back-feeding of liquid fractions comprisingmixtures of the inert solvent and the α,ω-C₃₋₁₀alkanediol mononitrateinto said distillation.

Preferably, said distillation is performed in an evaporator setup, evenmore preferably in an evaporated set-up comprising from 1 to 5evaporators, more preferably 2 to 4 evaporators. An exemplary, whilepreferred, evaporator set-up is outlined in FIG. 4 .

Said process preferably also comprises the isolation of theα,ω-C₃₋₁₀alkanediol mononitrate in a purity of at least 95 wt.-%,preferably at least 97 wt.-%, most preferably at least 98 wt.-%, as e.g.determined by GC chromatography using a FID detector.

Preferably, said isolated α,ω-C₃₋₁₀alkanediol mononitrate furthermorecomprises less than 1 of the inert solvent, more preferably less than0.5% of the inert solvent most preferably less than 0.1% of the inertsolvent.

The term ‘evaporator’ as used herein refers to a device used to turn aliquid form of a chemical substance or a mixture of chemical substance(such as the solution of the inert solvent and the α,ω-C₃₋₁₀alkanediolmononitrate) into its/their gaseous-form/vapor. It is well understood,that the liquid may also be only partially evaporated, or partiallyvaporized, into the gas form, while part of the liquid remains liquid.Said process can be used for the separation of mixtures, e.g. by partialevaporation and partial condensation as illustrated herein.

The term condenser as used herein refers to a device or unit used tocondense a gaseous substance or gaseous mixture into a liquid statethrough cooling.

In a particular advantageous embodiment, the solvent removal andrecovery according to the present invention comprises the followingsteps:

-   -   (S-1) Provision of an evaporator setup comprising 3 evaporators,    -   (S-2) Feeding of a solution comprising an α,ω-C₃₋₁₀alkanediol        mononitrate in an inert solvent (also referred to herein as S-I)        onto a first evaporator (FIG. 4 : E1) and applying a pressure of        400 to 600 mbar resulting in a gaseous phase (I) (also referred        to herein as GP-I) and a liquid phase (I) (also referred to        herein as LP-I), wherein said liquid phase (I) comprises from        about 70 to 95 wt.-% of the α,ω-C₃₋₁₀alkanediol mononitrate,    -   (S-3) Feeding said gaseous phase (I) onto a first (partial)        condenser (C1) to remove a first liquid fraction (also referred        to herein as LF-I) by cooling to a temperature of 20 to 40° C.,        preferably to a temperature of 20 to 35° C., more preferably to        a temperature of 25-30° C., while passing the remaining gaseous        phase (II) (also referred to herein as GP-II) onto a second        condenser (FIG. 4 : C2),    -   (S-4) Feeding the liquid phase (I) (LP-I) from step (S-2) onto a        second evaporator (FIG. 4 : E2) and applying a pressure of 50 to        150 mbar resulting in a gaseous phase (III) (also referred to        herein as GP-III) and a liquid phase (II) (also referred to        herein as LP-II), wherein the liquid phase (II) comprises more        than 95 wt.-%, preferably more than 97 wt.-%, most preferably        more than 98 wt.-% of the α,ω-C₃₋₁₀alkanediol mononitrate,    -   (S-5) Feeding the gaseous phase (III) onto a third (partial)        condenser (FIG. 4 : C3) to remove a second liquid fraction (also        referred to herein as LF-II) by cooling to a temperature of 10        to 30° C., preferably to a temperature of 20 to 30° C., more        preferably to a temperature of 20 to 25° C., while passing the        remaining gaseous phase (IV) (also referred to herein as GP-IV)        onto a fourth condenser (FIG. 4 : C4) to liquefy the inert        solvent, and    -   (S-6) Feeding the liquid phase (II) (LP-II) from step (S-4) onto        a third evaporator (FIG. 4 : E3) and applying a pressure of 5 to        10 mbar with the proviso that at least one of LF-I and LF-II is        fed back onto the first or the second evaporator.

It is well understood that the liquid fractions (I) and (I) stillcontain α,ω-C₃₋₁₀alkanediol mononitrate, which is recovered by saidback-feeding.

An exemplary (while preferred) removal and recovery process according tothe present invention is illustrated in FIG. 4 .

In a partial condensation according to this invention, a vapour stream(vaporized stream) is partially condensed (liquefied) in a condenser.The remaining (not condensed) vapor is passed to a subsequent (total)condenser operated at lower temperatures to almost liquefy the remainingsolvent.

Preferably, the amount of the α,ω-C₃₋₁₀alkanediol mononitrate in theinert solvent in step (S-2) is selected in the range from 10 to 50wt.-%, more preferably in the range from 20 to 40 wt.-%, which is e.g.obtainable from the hydrolysis as outlined above.

DESCRIPTION OF THE FIGURES

FIG. 1 : In the embodiment of FIG. 1 , an exemplary, but none limitingvessel cascade setup for the acylation process according to the presentinvention is shown:

The acylating agent (AA), the α,ω-alkanediol (AD) and water are fed intothe first vessel of a vessel cascade (V1) to form the reaction mixture(ARM). The reaction mixture (ARM) is then fed onto a first distillationcolumn (V2) and the acylating agent and water are distilled off to forma mixture (AM-I). The mixture (AM-I) is subsequently fed onto a seconddistillation column (V3) and the ‘recycled reaction components (I)’consisting essentially of α,ω-alkanediol mono- and diacylate (ADMA &ADDA) are distilled off to form a mixture (AM-Ia). The mixture (AM-Ia)is then fed onto a third distillation column (V4) and ADMA is distilledoff while recovering ‘recycled reaction components (II)’ consistingessentially of AD. During the process the recycled reaction components(I) and (II) are continuously re-fed into the first reaction vessel(V1). A small fraction (below 5%) of the recycled reaction components(I) and (II) can be purged/removed to avoid accumulation of possibleformed by-products if necessary. In addition, the acylating agent aswell as (part of) the water is re-fed as deemed appropriate into thefirst reaction vessel (V1).

FIG. 2 : In the embodiment of FIG. 2 , an exemplary, but none limitingcontinuously operated flow-reactor setup for the nitrate ester formationaccording to the present invention is shown:

The nitrating agent as well as part of the solution (B-I) consisting ofα,ω-C₃₋₁₀alkanediol monoacylate and the inert solvent are fed into afirst reactor (B1) followed by adding a second portion of the solution(B-I) into the second reactor (B2). The nitrate ester formation reactionmixture (NRM) obtained after reactor (B2) is quenched in reactor B3. Thethus obtained reaction biphasic mixture (NBM) is split into two phasesto obtain an organic (NOP) and an aqueous phase (NAP). Theα,ω-C₃₋₁₀alkanediol mononitrate monoacylate (ADMNMA) is in said organicphase and can be isolated thereof.

FIG. 3 : In the embodiment of FIG. 3 , an exemplary, but not limitingvertical, stirred cascade reactor setup for the hydrolysis processaccording to the present invention is shown.

The first (bottom) chamber (C1) is continuously loaded with a solutionconsisting essentially of an α,ω-C₃₋₁₀alkanediol mononitrate monoacylateand an inert solvent (HS-I) (such e.g. with the NOP obtained as outlinedin FIG. 2 ) and an aqueous solution of a base to form a reaction mixture(HRM). The reaction mixture (HRM) is transferred into a second vessel(C2) for phase separation resulting in an organic phase (HS-II) and anaqueous phase (HS-III). The organic phase is transferred to a evaporatorsetup (C4) for isolation of the α,ω-C₃₋₁₀alkanediol mononitrate (ADMN)The aqueous phase (HS-III) is transferred into a third vessel (C3) forfurther extraction with the inert solvent to obtain an organic phaseHS-IV) which is also transferred (combined with HS-II) to the evaporatorsetup (C4) to recover further ADMN.

FIG. 4 : In the embodiment of FIG. 4 , an exemplary, but none limitingevaporator setup for the removal and recovery of the inert solventaccording to the present invention is shown: A solution comprising anα,ω-C₃₋₁₀alkanediol mononitrate in an inert solvent (S-I) is fed onto afirst evaporator (E1) and a first liquid fraction (LF-I) is removed fromthe distillate of evaporator (E1) through partial condensation in afirst condenser (C1) while the remaining vapors pass onto a secondcondenser (C2) to liquefy the remaining inert solvent (S). The liquidphase (LP-I) from evaporator (E1) is fed onto a second evaporator (E2).A second liquid fraction (LF-II) is removed from the distillate ofevaporator (E2) through partial condensation in a condenser (C3), whilethe remaining vapors (GP-IV) pass onto a fourth condenser (C4) toliquefy the remaining inert solvent. The liquid phase (LP-II) fromevaporator (E2) is fed into a third evaporator (E-3) to remove theremaining inert solvent and to recover the pure α,ω-C₃₋₁₀alkanediolmononitrate.

EXAMPLE

A) Acylation

-   -   The acetylation (equilibrium formation) was performed either        batchwise without recycles or in a vessel cascade setup in a        fully continuous process, by feeding the starting materials into        a first vessel. The resulting reaction mixture from the last        vessel is fed onto a first distillation column for separation        (removal) of H₂O/HAc from PDDA/PDMA/PD. This mixture of        PDDA/PDMA/PD is fed to a second rectification column for removal        of PDDA from PD/PDMA. This mixture of PD/PDMA is fed to a third        rectification column for separation of PDMA from PD.    -   Pure PDMA was obtained by rectification. Recovered PDDA, PD and        HAc were recycled and fed back together with the adjusted amount        of water to the reaction vessel cascade, allowing for an overall        yield of 90%.    -   Aa) Without Using Recycling Streams (Comparative)        1,3-Propanediol (PD, 14.0 kg, 0.18 kmol, 99.7%) was mixed with        Acetic Acid (HAc, 9.8 kg, 0.16 kmol, 100%). After inerting of        the reactor by nitrogen flow, strirring was started (500 rpm)        and the jacket temperature was increased from 20° C. to 135° C.        within 70 minutes and kept at 135° C. at 4 hours and at reflux        of reaction mixture. After 4 hours the jacket temperature was        set to 100° C. and the pressure is slowly reduced to approx. 100        mbar abs. while removing 1.55 kg distillate. 22.0 kg residue        were obtained comprising a mixture of acetic acid, water,        unreacted PD (28 wt %), 3-acetylpropan-1-ol (PDMA, 44.1 wt %)        and 1,3-propanedioldiacetate (PDDA, 11.3 wt %). Yield of PDMA        was 44.4% and of PDDA was 8.5% based on PD.    -   Removal of acetic acid/water was performed at 50 mbar abs top        pressure in a rectification column DN50 with 3.5 m BX packing        equipped with condenser, liquid separator for reflux adjustment        and falling film evaporator with a feed rate of 6.7 kg/h and        reflux ratio of 0.4-0.5 resulting in a top take off of 1.1 kg/h        containing acetic acid and water and s sump stream of 5.6 kg/h        (34 wt % PD, 52 wt % PDMA, 13 wt % PDDA).    -   Removal of PDDA was performed at 20 mbar abs top pressure in a        rectification column DN50 with 3.5 m BX packing equipped with        condenser, liquid separator for reflux adjustment and falling        film evaporator with a feed rate of 1.6 kg/h and reflux ratio of        7-8 resulting in a top take off of 0.4 kg/h containing 1 wt %        PD, 40 wt % PDMA, and 54 wt % PDDA. The corresponding sump        stream (1.2 kg/h) consisted of 44 wt % PD, 55 wt % PDMA, 0.3 wt        % PDDA.    -   Separation of PDMA from PD was performed at 20 mbar abs top        pressure in a rectification column DN50 with 3.5 m BX packing        equipped with condenser, liquid separator for reflux adjustment        and falling film evaporator with a feed rate of 1.2 kg/h and        reflux ratio of 3-4 resulting in a top take off of 0.6 kg/h        containing 0.5 wt % PD, 97-98 wt % PDMA, and 1 wt % PDDA. The        corresponding sump stream (0.6 kg/h) consisted of 91-92 wt % PD,        8-9% PDMA. Overall Yield of PDMA during the three rectification        steps was 71-73%.    -   Overall yield of PDMA (reaction and rectification steps) based        on PD was 31-33%.    -   Ab) using recycling streams in fully continuous mode (inventive)    -   1,3-Propanediol (PD, 76 kg/h, 0.99 kmol/h, 99.7%) was mixed with        fresh Acetic Acid (HAc, 57 kg/h, 100%), 89 kg/h distillate from        the first rectification column (56 wt % acetic acid, 44 wt %        water), 90 kg/h distillate of the 2^(nd) rectification column (2        wt % PD, 36.5 wt % PDMA, 61 wt % PDDA) and 110 kg/h sump stream        from the third rectification column (97 wt % PD, 3% PDMA). The        reaction was performed in a continuous stirred tank reactor at        reflux temperature (atmospheric pressure) with a mean residence        time of 5-6 hours to deliver 400 kg/h reaction mixture (mixture        of acetic acid, water, unreacted PD (29 wt %),        3-acetylpropan-1-ol (PDMA, 35 wt %) and 1,3-propandioldiacetate        (PDDA, 14.5 wt %)). Removal of acetic acid/water was performed        at 50 mbar abs top pressure in a rectification column DN500 with        3.7 m BX packing equipped with condenser, liquid separator for        reflux adjustment and falling film evaporator with a feed rate        of 400 kg/h and reflux ratio of 0.5-1 resulting in a top take        off of 85 kg/h containing acetic acid and water and sump stream        of 315 kg/h (36 wt % PD, 45 wt % PDMA, 19 wt % PDDA).    -   Removal of PDDA was performed at 20 mbar abs top pressure in a        rectification column DN1000 with 10.8 m BX packing equipped with        condenser, liquid separator for reflux adjustment and falling        film evaporator with a feed rate of 315 kg/h and reflux ratio of        10-15 resulting in a top take off of 92 kg/h containing 2 wt %        PD, 36.5 wt % PDMA, and 61 wt % PDDA. The corresponding sump        stream (223 kg/h) consisted of 50 wt % PD, 48-49 wt % PDMA, 1-2        wt % PDDA.    -   Separation of PDMA from PD was performed at 10 mbar abs top        pressure in a rectification column DN1000 with 7.5 m BX packing        equipped with condenser, liquid separator for reflux adjustment        and falling film evaporator with a feed rate of 223 kg/h and        reflux ratio of 5-10 resulting in a top take off of 108 kg/h        containing 0.1 wt % PD, 98-99 wt % PDMA, and 1 wt % PDDA. The        corresponding sump stream (115 kg/h) consisted of 98-99 wt % PD,        1-2% PDMA.    -   Overall yield of PDMA (reaction and rectification steps) based        on (fresh) PD was 90%.

B) Nitrate Ester Formation

-   -   A 40% w/w solution of PDMA in Dichloromethane (DCM) was reacted        at 5° C. in a flow-reactor with Nitrosulfonic acid (1.1 eq HNO₃,        2.2 eq H₂SO₄, less than 3 wt % water).    -   The nitrate ester formation reaction was performed in a        continuously operated flow-reactor, by mixing PDMA in DCM (60 wt        % DCM/40 wt % PDMA) with Nitrosulfuric acid in a constant ratio        and a steady flow of both components. To control the reaction        temperature below 40° C., the reaction was partitioned by        massflow between two serial flow-reactors by feeding PDMA in 2        portions (reactor 1/reactor 2=40%:60%). The overall residence        time in both reactors was kept at 15-19 seconds.    -   Directly after the 2 sequential reactors, the reaction was        diluted/quenched with water at 10° C., followed by a phase        separation. The organic phase, containing the intermediate        3-acyl-propan-1-nitrate (MAMN) was washed once with water,        stabilizing the mixture for intermediate storage in a buffer        tank. The organic phase, containing MAMN can be subjected as-is        to the next step or optionally washed with water prior to the        next step, with an overall yield of 99%    -   The aqueous phase consisting mainly of diluted H₂SO₄ was        concentrated to 65 or 96% H₂SO₄ for use in other applications.

C) Hydrolysis

-   -   PDMNMA (ca 50% in DCM) was reacted at 40-56° C. with 1,3 eq.        NaOH (10-11% solution in water).    -   The hydrolysis of PDMNMA was performed in a vertical, stirred        cascade reactor, by continuously feeding PDMNMA (ca 50% in DCM)        together with 10-11% NaOH solution (in a ratio 1/1.3 eq.) from        the bottom. Residence time was 4 hours, at a reaction        temperature of 40-56° C. After complete conversion (>99.9%), the        phases were cooled to appr. 20° C., split, and the aq. phase was        washed/extracted in continuous mode with DCM (back-extraction of        PDMN) at room temperature. The combined organic phases were        subjected to solvent removal (see D) Workup).    -   The desired product is obtained in 97% yield, after removal of        DCM from the combined organic phases.

D) Solvent Removal and Recovery (Partial Condensation)

-   -   After hydrolysis, the combined organic phases PDMN/DCM (77% DCM)        were subjected to solvent removal in a 3-stage evaporator setup,        by feeding the organic phases into a first evaporator where PDMN        solution (containing 7-8% DCM) was produced at 500 mbar. The        distillates (vapour stream) were directed to a partial        condenser, where a liquid fraction (PDMN/DCM, ca. 55-60% PDMN)        was recovered at 30° C. and fed back to the first evaporator.        The remaining vapors passed to a (total) condenser operated at        0° C. to recover DCM in high purity (<0.03% PDMN).    -   The PDMN solution from the first evaporator (containing 7-8%        DCM) is fed to a second evaporator operated at 100 mbar to        produce a liquid solution containing ca. 1 wt % DCM. The        distillates (vapour stream) were directed to a partial        condenser, where a liquid fraction (PDMN/DCM, ca. 70-75% PDMN)        was recovered at 15° C. and fed back to the first evaporator.        The remaining vapors passed to a (total) condenser operated at        0° C. to recover DCM (ca. 0.1% PDMN).    -   The PDMN solution from the second evaporator (containing ca. 1%        DCM) is fed to a third evaporator operated at 10 mbar to produce        a liquid solution containing less than 0.1 wt % DCM. The        distillates (vapour stream) were directed to a partial        condenser, where a liquid fraction (PDMN/DCM, ca. 90% PDMN) was        recovered at 0° C. and fed back to the first evaporator. The        remaining vapors were discarded.

1. A continuous process for the two-phase hydrolysis ofα,ω-C₃₋₁₀alkanediol mononitrate monoacylates, said process comprisingcontinuously feeding a base and a solution comprising anα,ω-C₃₋₁₀alkanediol mononitrate monoacylate and an inert solvent into astirred cascade reactor.
 2. The hydrolysis process according to claim 1,wherein the base is selected from the group of NaOH, KOH, Ca(OH)₂ orammonia or an aqueous solution thereof, preferably the base is anaqueous solution of NaOH.
 3. The hydrolysis process according to claim1, wherein the concentration of the base in the aqueous solution isselected in the range from 1 and 50 wt.-%, more preferably from 5 and 30wt.-%, most preferably from 7.5 and 15 wt.-%.
 4. The hydrolysis processaccording to claim 1, wherein the reaction temperature is selected inthe range from 20 to 70° C., preferably from 30 to 60° C., and mostpreferably from 40 to 56° C.
 5. The hydrolysis process according toclaim 1, wherein 1 to 1.5 mol equivalents, more preferably 1.1 to 1.3mol equivalents, most preferably 1.3 mol equivalents of the base, basedon the α,ω-C₃₋₁₀alkanediol mononitrate monoacylate is used.
 6. Thehydrolysis process according to claim 1, wherein the hydrolysis iscarried out for a reaction time ranging from about 2 to about 6 hours,preferably from about 3 to about 5 hours, most preferably for about 4hours.
 7. The hydrolysis process according to claim 1, wherein theprocess is used for the preparation of an α,ω-C₃₋₁₀alkanediolmononitrate, preferably 3-nitrooxypropane-1-ol, said process furthercomprising the preceding steps (A) and (B) consisting of (A) Acylationof an α,ω-alkanediol, with an acylation agent (acylation reaction), saidacylation comprising the step of re-feeding recycled reaction componentscomprising α,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate andα,ω-C₃₋₁₀alkanediol diacylate back into said acylation reaction and withthe proviso that in the acylation reaction per mole recycled acylategroups 0.5 to 1.5 mole of water is added and that the molar ratio of the(molar) sum of the acylating agent, α,ω-C₃₋₁₀alkanediol monoacylate and2 times of α,ω-C₃₋₁₀alkanediol diacylate to the sum of theα,ω-C₃₋₁₀alkanediol, α,ω-C₃₋₁₀alkanediol monoacylate andα,ω-C₃₋₁₀alkanediol diacylate is selected in the range from 0.5 to 1.1mol per mol of α,ω-C₃₋₁₀alkanediol to obtain a α,ω-C₃₋₁₀alkanediolmonoacylate, (B) Continuous nitrate ester formation of theα,ω-C₃₋₁₀alkanediol monoacylate by reacting a nitrating agent with asolution comprising the α,ω-C₃₋₁₀alkanediol monoacylate and an inertsolvent in a group of pieces of equipment comprising at least tworeactors in series by simultaneously feeding said solution into thefirst and the second reactor to obtain the respectiveα,ω-C₃₋₁₀alkanediol mononitrate monoacylate, and optionally theconsecutive step (D) (D) Removal and recovery of the inert solvent fromthe solution by distillation, said process comprising partialcondensation and continuous back-feeding of liquid fractions comprisingmixtures of inert solvent and α,ω-C₃₋₁₀ alkanediol mononitrate into saiddistillation.
 8. The process according to claim 7, wherein the acylationstep (A) is a continuous process carried out in a vessel cascade set-up.9. The process according to claim 7, wherein the acylation step (A)comprises the step of separation of the α,ω-C₃₋₁₀alkanediol monoacylatesuch that a) the amount of α,ω-C₃₋₁₀alkanediol in theα,ω-C₃₋₁₀alkanediol monoacylate is less than 0.5 wt.-% and/or b) theamount of the α,ω-C₃₋₁₀alkanediol diacylate in the α,ω-C₃₋₁₀alkanediolmonoacylate is less than 5 wt. %.
 10. The process according to claim 7,wherein the acylation agent in step (A) is selected from the group ofcarboxylic acids and/or derivatives thereof, more preferably of linearor branched C₁₋₄ carboxylic acids, most preferably the acylation agentis acetic acid.
 11. The process according to claim 7, wherein in thecontinuous nitrate ester formation of step (B) the mass flow of thesolution into the first reactor is selected in the range of 40 to 60% ofthe total mass flow of the solution, while the remaining solution is fedinto the second reactor.
 12. The process according to claim 7, whereinin the continuous nitrate ester formation of step (B) the concentrationof the α,ω-C₃₋₁₀alkanediol monoacylate in the inert solvent is selectedin the range from 10 and 60 wt.-%, more preferably from 20 and 50 wt.-%and most preferably from 35 and 45 wt.-%.
 13. The process according toclaim 7, wherein in the continuous nitrate ester formation of step (B)the nitrating agent is a mixture of H₂SO₄ and HNO₃, wherein a) the molratio of HNO₃ to the α,ω-C₃₋₁₀alkanediol monoacylate is selected in therange from 1 to 1.5, preferably from 1.1 to 1.2 and b) the mole ratio ofthe H₂SO₄ to the HNO₃ is selected in the range from 1.5 to 2.5,preferably from 1.7 to 2.3, most preferably from 1.9 to 2.0.
 14. Theprocess according to claim 7, wherein in the continuous nitrate esterformation of step (B) the reaction volume of the first reactor to thesecond reactor is selected in the range from 4:1 to 1:4, preferably from3:1 to 1:3, most preferably from 2:1 to 1:2.
 15. The process accordingto claim 7, wherein in the continuous nitrate ester formation of step(B) the nitrate ester formation is carried out for a mean residence timefor the two reactors ranging from about 5 to about 30 seconds,preferably from about 10 to about 20 seconds, most preferably from about15 to 19 seconds.